1. Field of the Invention
This invention relates to the fabrication of devices relying on magnetic properties and, more particularly, to the fabrication of devices relying on uniaxial anisotropy in a garnet layer.
2. Art Background
Devices relying on magnetic properties often require the deposition of a metal film during their fabrication. For example, in the case of magnetic bubble devices, i.e., devices based on uniaxial magnetic domains, in aluminum alloy is deposited on a silicon dioxide layer that, in turn, overlays the magnetic garnet epilayer. These metallic films are patterned to produce a desired result in a localized area of the device. In the example of magnetic bubble devices, the aluminum alloy does not cover the entire silicon dioxide layer, but is confined to areas where control functions are performed, e.g., the metal film is patterned to induce bubble nucleation, replication or transfer in a particular area of the magnetic garnet film at a given instant in time.
Since the metallic films utilized are not continuous, but are localized in particular areas of the devices, subsequent deposited layers will not fill in the steps produced by this localization. Thus, continuing the example of magnetic bubble devices, if a second insulating layer, e.g., another layer of silicon dioxide is deposited over the aluminum alloy, this silicon dioxide layer will not be planar, but will have depressions in areas where the underlying aluminum alloy is absent. Subsequently a material such as permalloy which will be patterned in a configuration suitable for controlling domain propagation is deposited onto this second insulating layer. The domain propagation control layer thus formed is, in turn, non-planar.
This non-planar structure, although usually unimportant in semiconductor devices, often becomes significant in devices which rely on magnetic properties. Since magnetization is a three dimensional effect, a film that is not planar experiences magnetic gradients through its cross-section. For example, as discussed in the case of magnetic bubble devices, if a permalloy alloy is deposited on a stepped silicon dioxide film, this permalloy alloy is similarly non-planar. When magnetic fields are introduced to operate the device, various areas of the permalloy strip experience spurious magnetic effects. This results in a degree of device unreliability. (See, for example, W. Strauss, Journal of Applied Physics, 49 pp. 1897-1899, March (1978).)
In addition to the reliability problems described above, other difficulties often are encountered. For example, after the permalloy layer is deposited, it must be patterned. This patterning is typically done by exposing through a mask a layer of photoresist deposited on the permalloy. The mask used to produce this patterned feature must be registered relative to the pattern of the underlying metallic structures. Typically, the mask must be moved several times to achieve this registration. Each movement of the mask results in abrasion between the photoresist and the mask. This abrasion induces defects in the photoresist and in the permalloy pattern it defines, causing reduced reliability of the device.
Additionally, after the deposition of the initial insulating layer, e.g., silicon dioxide, and the overlying metal layer, the garnet with its deposited layers must be removed from the deposition apparatus in order to etch the metal to form the desired pattern for functions such as replication. After this etching is completed, a second insulating layer and a layer for controlling propagation are deposited. However, invariably some foreign matter is introduced between the metal layer and subsequently deposited layers. To improve yield and reliability, it is desirable to minimize this contamination problem.